Glioblastoma multiforme (GBM) is the most common form of malignant glioma and is characterized by marked genetic instability, extensive intra-tumoral histopathological variability, and unpredictable variation in its clinical behavior. We investigated global gene expression in surgical samples of primary brain tumors. Gene expression profiling revealed large differences between normal brain samples and tumor tissues and between GBMs and lower grade oligodendroglial tumors. Extensive differences in gene expression were found among GBMs, particularly in genes involved in angiogenesis, immune cell infiltration, and extracellular matrix re-modeling. Significantly, we found that the global gene expression patterns in paired specimens from the same GBM invariably were more closely related to each other than to any other tumor, even when the paired specimens had strikingly divergent histologies. Survival analyses revealed a set of approximately 70 genes that were more highly expressed in rapidly progressing tumors and which stratified GBMs into two groups that differed by more than four-fold in median duration of survival. We further investigated one gene from the group, FABP7, and confirmed its association with survival in two unrelated cohorts totaling 105 patients. Expression of FABP7 enhanced the motility of glioma-derived cells in vitro. Our analyses thus provide a series of prognostic markers and suggest that their expression may enhance the invasive potential of tumor cells.